In open root welding of pipe lines and other delicate electric arc welding operations it has proved beneficial to use a proprietary arc welding process having an arc condition and a short circuit condition in each of a plurality of low frequency welding cycles, such as less than about 200 cycles per second. The power supplied to the welding electrode in such process is controlled according to a detected short circuit and the anticipation of the metal breaking during the short circuit condition. This short circuit welding process accurately controls heat and drastically reduces spatter. It is referred to in the welding industry as the proprietary STT welding process of The Lincoln Electric Company and is performed by a welder having a power source wherein an output power switch is open at initiation of the short circuit condition and opened to subsequently initiate the arc condition after a short circuit. Such welder is normally manufactured with a maximum capacity of approximately 300-500 amperes. Consequently, the welder has a limited deposition rate. There is a need for a welding system to perform the proprietary welding process, but having a substantially greater maximum current rating. Heretofore, this increased current capacity was obtainable only by designing a special power source and output switch machine. The switch had to have a drastically higher current capacity and the remainder of the power source had to have a substantially greater current generating capacity. These requirements substantially increased the cost, which cost was not justified due to substantially less applications. The concept of paralleling power sources was not practical because each of the power sources would produce its own waveform, which resulted in an unacceptable welding result. Thus, there is a need for an inexpensive welding system to perform the proprietary welding process using a short circuit condition and an arc condition with a current capacity substantially greater than 300-500 amperes.